Recently, there has been a rapid increase in the transmission and/or storage of image information and the like. This has been especially true in the use of facsimile. Additionally, use of high resolution monitors for generating a soft copy and/or browsing of the image information has resulted in additional requirements being placed on digital transmission and/or storage interfaces. In certain applications, rapid progression from a low resolution replica to a high resolution image is desirable and sometimes necessary. In order to improve encoding/decoding efficiency and speed, prior arrangements were employed which decomposed a high resolution image into a lower resolution replica and so-called supplemental information. The supplemental information was required to later recompose the low resolution replica into the high resolution image. In one known prior arrangement, supplemental information was generated only for pixels (picture elements) determined to be in a predetermined relation with their neighboring pixels, i.e., at an edge. Pixels that no not satisfy the above condition but that were determined to require supplemental information were forced to satisfy the above condition by modifying the image reduction rules. That is, the reduction rules were modified to force a pixel to satisfy the above condition whenever the prediction rules would cause a decoder to otherwise improperly recompose the high resolution image. See, for example, our co-pending U.S. patent application Ser. No. 146,998, filed Jan. 22, 1988 now U.S. Pat. No. 4,870,497 issued Sept. 26, 1989 for one such prior arrangement.
A serious limitation of such a prior arrangement is that the prediction rules used to determine if supplemental information was required to be generated and encoded were based and dependent on the particular properties of the image reduction rules. Therefore, if the image reduction rules were changed, the prior prediction rules could not be used. Thus, any change in the image reduction rules would require development of a new set of prediction rules. This interdependence of the image reduction rules and the prediction rules is undesirable.
More recently, as disclosed in our co-pending U.S. patent application Ser. No. 359,909, filed concurrently herewith, the interdependence between the reduction rules and the prediction rules was eliminated. This is achieved by employing so-called general prediction rules to determine if the pixels to be recomposed are so-called typically predictable or non-typically predictable. Typically predictable pixels which would be improperly recomposed by using the general prediction rules are identified as exceptions. The non-typically predictable pixels and the typically predictable pixels that are exceptions require supplemental information to properly be recomposed. An exception was required to accompany each pixel identified as an exception. This, in turn, required the encoding and, subsequent, decoding of the exceptions. This encoding and decoding caused complexity and was inefficient. Thus, although the arrangement disclosed in our co-pending U.S. patent application Ser. No. 359,909, cited above, operates satisfactorily in many applications, its complexity and inefficiency renders it undesirable for other applications.